On Jun 3, 8:31 pm, jianhua li <lijh...@yahoo.com.cn> wrote:> In many text books, they say that the complememt of context free> language us not context free language . But they do not say the> complemet of CFL is context sensitive language or Recursively> enumerable language ? So what is the language of the complement of> context free language?

Complement of CFL could possibly be CFL but not necessarily is.
Complement of CFL is both recursive (R) and recursively enumerable
(RE). Why? All CFLs are both R and RE. R languages are closed under
complement (but RE are not). In that context, complement of CFL is R
which is inherently RE.